1. Field of the Invention
The invention in general relates to monitoring apparatus, and particularly to apparatus which will automatically diagnose a system malfunction, with a certain degree of probability.
2. Description of the Prior Art
The operating condition of various systems must be continuously monitored both from a safety and economic standpoint so as to obtain an early indication of a possible malfunction so that corrective measures may be taken.
Many diagnostic systems exist which obtain base line standards for comparison while the system to be monitored is running under normal conditions. The monitored system will include a plurality of sensors for obtaining signals indicative of certain predetermined operating parameters and if the monitored system includes rotating machinery, the sensors generally include circuits for performing real time spectrum analysis of vibration signals.
The totality of sensor signals are continuously examined and if any of the signals should deviate from the base line standard by a predetermined amount, an indication thereof will be automatically presented to an operator. Very often, however, the signal threshold levels are chosen at a value such that it is too late to take adequate protective measures once an alarm has been given. If, however, the threshold levels are set lower, they may be at a value such that an alarm is given prematurely and even unnecessarily. A shutdown of an entire system based upon this premature malfunction diagnosis can represent a significant economic loss to the system operator.
One type of diagnostic apparatus proposed, presented an operator with the probability of a malfunction based upon certain measured parameters. The malfunction probabilities presented to the operator, however, were still based upon certain signals exceeding or not exceeding a preset threshold level.
Another proposed diagnostic arrangement had for an object the display of a continuous indication of the probability as a malfunction. This proposed arrangement was predicated upon estimated failure rates and certain multivariate probability density functions describing specific malfunctions related to the totality of measurements. Such rates and functions, however, are extremely difficult, if not impossible, to obtain.
The diagnostic apparatus of the present invention will present to an operator a continuous indication of the probability of a malfunction based on two or more sensor readings, and not dependent upon simply exceeding selected threshold levels, so that the operator may be given an early indication and may be continuously advised of an increasing probability of one or more malfunctions occurring.